PCB calculators / Power
Free tool · PreBuild Engineering
LDO and linear regulator thermal calculator
Find out whether your LDO will overheat, and the most current it can safely deliver.
Inputs
V
V
mA
mA
°C/W
From the datasheet, for your package and copper area
°C
°C
Result
—
Why it matters
An LDO burns the voltage difference as heat. 5 V to 3.3 V at 500 mA is 0.85 W, enough to push a SOT-23 well past its limit. Datasheet θJA values assume a specific test board; small real boards are often worse.
Formula
P = (Vin − Vout) · Iload + Vin · Iq
Tj = Ta + P · θJA
I_max = ((Tj,max − Ta)/θJA − Vin·Iq) / (Vin − Vout)
Design tips
- Use the highest input voltage the regulator will ever see.
- Copper pour connected to the tab or exposed pad lowers θJA a lot.
- Above roughly 0.5–1 W, a buck converter is usually the better choice.
Results are engineering estimates from standard formulas and published approximations. Always confirm against component datasheets, your fabricator's capabilities and, for critical designs, simulation or measurement.